Gastrointestinal Tract

Stomach Morphine and other m agonists usually decrease gastric acid secretion, although stimulation sometimes occurs. Activation of opioid receptors on parietal cells enhances secretion, but indirect effects, including increased secretion of somatostatin from the pancreas and reduced release of acetylcholine, predominate in most circumstances. Low doses of morphine decrease gastric motility, prolonging gastric emptying time; this can increase the likelihood of esophageal reflux. The tone of the antral portion of the stomach and of the first part of the duodenum is increased, which can make therapeutic intubation of the duodenum more difficult. Passage of the gastric contents through the duodenum may be delayed by as much as 12 hours, and the absorption of orally administered drugs is retarded.

Small Intestine Morphine diminishes biliary, pancreatic, and intestinal secretions and delays digestion of food in the small intestine. Resting tone is increased, and periodic spasms are observed. The amplitude of the nonpropulsive type of rhythmic, segmental contractions usually is enhanced, but propulsive contractions are decreased markedly. The upper part of the small intestine, particularly the duodenum, is affected more than the ileum. A period of relative atony may follow the hypertonicity. Water is absorbed more completely because of the delayed passage of bowel contents, and intestinal secretion is decreased; this increases the viscosity of the bowel contents.

Large Intestine Propulsive peristaltic waves in the colon are diminished or abolished after administration of morphine, and tone is increased to the point of spasm. The resulting delay in the passage of bowel contents causes considerable desiccation of the feces, which, in turn, retards their advance through the colon. The amplitude of the nonpropulsive type of rhythmic contractions of the colon usually is enhanced. The tone of the anal sphincter is augmented, and reflex relaxation in response to rectal distension is reduced. These actions, combined with inattention to the normal sensory stimuli for defecation reflex owing to the central actions of the drug, contribute to morphine-induced constipation.

BILIARY TRACT After the subcutaneous injection of 10 mg morphine sulfate, the sphincter of Oddi constricts, and the pressure in the common bile duct may rise more than tenfold within 15 minutes; this effect may persist for 2 hours or more. Fluid pressure also may increase in the gallbladder, producing symptoms that vary from epigastric distress to typical biliary colic. All opioids can cause biliary spasm. Atropine only partially prevents morphine-induced biliary spasm, but opioid antagonists prevent or relieve it. Nitroglycerin (0.6-1.2 mg) administered sublingually also decreases the elevated intrabiliary pressure.

Was this article helpful?

0 0
Constipation Prescription

Constipation Prescription

Did you ever think feeling angry and irritable could be a symptom of constipation? A horrible fullness and pressing sharp pains against the bladders can’t help but affect your mood. Sometimes you just want everyone to leave you alone and sleep to escape the pain. It is virtually impossible to be constipated and keep a sunny disposition. Follow the steps in this guide to alleviate constipation and lead a happier healthy life.

Get My Free Ebook


Post a comment